1. Field of the Invention
The invention relates to a driving an tensioning device for a flexible protective strip or curtain, comprising a rolling-up driving-shaft from which and onto which unrolls and rolls up said protective strip, and an unrolling driving-shaft acting on the flexible protective strip or curtain for unfolding same, the rolling-up driving-shaft and the unrolling driving-shaft being each driven in rotation by means of a motor associated with braking means.
2. Description of the Prior Art
There is already known a driving device for a flexible protective strip or curtain-type member meeting the above description. Thus, this driving device includes a rolling-up driving-shaft from which and onto which unrolls and rolls up the flexible member. This rolling-up driving-shaft is driven in rotation through a tubular-type motor or the like, this during this phase of rolling up of the flexible member. It should be noted that this motor is provided with an electromagnetic brake which is activated, i.e., it does no longer brake, when the motor it is associated with is in operation, i.e., rolling up, but also during the phase of unfolding controlled by the unrolling driving-shaft. As a matter of fact, like the rolling-up driving-shaft, this latter cooperates with a motor which ensures its driving in rotation during the phase of unfolding of the protective member. Here too, with this motor is associated an electromagnetic brake which is activated, i.e., which does no longer brake, as soon as one of the motors of the rolling-up driving-shaft or unrolling driving-shaft is under power.
Moreover, in this particular case, the rolling-up driving-shaft and the unrolling driving-shaft are arranged parallel to each other on both sides of the surface to be covered by means of the flexible protective member. Furthermore, this latter is initially rolled up onto the rolling-up driving-shaft and includes, at the height of its free end, straps joining the unrolling driving-shaft where they roll up onto drums this latter is provided with.
As a matter of fact, this kind of flexible protective member is aimed at unfolding in a nearly horizontal or slightly inclined position above the surface to be protected. Therefore, this raises the problem of the tensioning of this flexible member and its maintaining in such a position. Under its own weight, this flexible protective member indeed necessarily sags between the rolling-up driving-shaft and the unrolling driving-shaft, more particularly during the unfolding phase. It should indeed be reminded that during the operation of one of the motors the brakes associated to each of them are activated to enable free rotation of the rolling-up driving-shaft and the unrolling driving-shaft.
Therefore, in order to take up the slack of the flexible protective member upon unfolding, it is intended to control the operation, during a short time, of either the motor of the unrolling driving-shaft or that of the rolling-up drivingshaft. More particularly, during this short time, either the rolling-up driving-shaft or the unrolling driving-shaft, as the case may be, of the motor which is not activated is not driven in rotation because of its inertia. Consequently, there occurs no additional unrolling of either the protective member or the straps, but a mere taking up of the slack at the level of this untensioned flexible protective member. Consequently, upon the complete standstill of the motors, the brakes are deactivated and impede rotation in any direction of this rolling-up driving-shaft and the unrolling driving-shaft, to finally keep the flexible protective member tensioned.
Practical experience shows that this process is not merely theoretical, that is, for the process to work the backlash to be taken up to ensure the tensioning of the flexible protective member should be small, for otherwise the period of time during which one of the motors is actuated to ensure this tensioning is either too short or too long, so that the unrolling of said flexible protective member or the straps connected to the unrolling driving-shaft cannot simultaneously be impeded.
In order to improve the driving device as described above, there has been imagined to associate with the rolling-up driving-shaft, and auxiliary brake capable of producing a torque withstanding the rotation of this rolling-up driving-shaft during the unfolding of the protective member. More particularly, through such a resisting couple the traction which has to be exerted on the straps through the driving in rotation of the unrolling driving-shaft is higher, so that the protective member is maintained tensioned during its unfolding.
This auxiliary brake may be of a mechanical or Foucault-current type. As a matter of fact, a Foucault-current brake is efficient as soon as there exists a rotation. As a result, it can give rise to a slackening of the protective member at the end of the unfolding stroke. Therefore, it only partly solves the above-mentioned problem. A mechanical brake of the friction type often integrates a ratchet wheel so as not to enter into operation in a determined direction of rotation, i.e., in the direction of rotation followed by the rolling-up phase. Such a mechanical brake which provides a solution for the disadvantages experienced with a Foucault-current brake, however, proves particularly complex and leads to a substantial increase of the cost price of the driving device.
To this should be added that if one not only wants to ensure that the flexible protective member be tensioned when in unfolded position, but also that the straps be so once said flexible protective member has been completely or partially rolled up, it is necessary to provide both the rolling-up driving-shaft and the unrolling driving-shaft with such an auxiliary brake. One may of course imagine to combining the systems so that, after rolling-up of the flexible protective member, the motions are inverted for a short period of time by a control of the rotation of the unrolling driving-shaft, in order to obtain the tensioning of the straps. As a result, these solutions are uneconomical in one case and unpractical to be used in the other case.
Such problems of tensioning, or more particularly of keeping tensioned, are also experienced with respect to flexible protective members, of the roller blind type, the skirt of which has a nearly horizontal movement or at least with an insufficient slanting for its unfolding to occur under its own weight.
By way of an example, such a roller blind includes a rolling-up driving-shaft for the skirt rotatingly mounted in a box inside which is also fitted the unrolling driving-shaft for this skirt. As a matter, this latter is arranged below the rolling-up driving-shaft and includes, at its ends, tooth wheels engaging into openings provided for at the ends of the blades said skirt is comprised of. Thus, during the unfolding, the unrolling driving-shaft is driven in rotation through a motor which is associated to same. It also includes a brake which is activated, i.e., which does not brake when the motor is actuated and, conversely, impedes the unrolling driving-shaft from rotation in the event the motor stops operating, so as to lock in down movement the skirt of the roller blind. The brake is also activated so as not to brake any longer during the driving in rotation of the rolling-up driving-shaft through the motor which is particular to same. In this kind of configuration, this rolling-up driving-shaft for the skirt is often without electromagnetic brake. As already stated, the locking of the skirt is indeed obtained through the braking motor the unrolling driving-shaft is fitted with. Therefore, the rolling-up driving-shaft is not subjected to a large torque corresponding to the total weight of the skirt.
In addition, the motor of this rolling-up driving-shaft is associated with auxiliary braking means. Thus, the reduction gear provides a braking force capable of opposing the rotation of the rolling-up shaft under the influence of the reduction torque produced by the few blades of the skirt between the unrolling driving-shaft and that rolling-up driving-shaft.
As already stated above, the skirt of such roller blinds is made of a juxtaposition of blades which are not only hingedly jointed to each other, but are often also telescopic in a direction which is perpendicular to same, so as to be capable of imparting to the skirt an openwork position. More particularly, when the blades are kept separated from each other, they leave openings allowing light rays to pass through. As a matter of fact, this kind of telescopic jointing of the blades of a roller-blind skirt gives rise to large difficulties, in particular within the framework of roller blinds with nearly horizontal unfolding. More particularly, such roller blinds are applied to roof windows or the like. Therefore, they are particularly exposed to the elements. Thus, despite the presence of ta protective box, moisture can penetrate into the joints of the blades located inside this box and, of the blades extending between the rolling-up driving-shaft and the unrolling driving-shaft. Now, in the event of frost, this moisture becomes ice which clamps the joints of these blades, while it is just between this rolling-up driving-shaft and the unrolling driving-shaft that said joint is normally under highest strain. Therefore, when the user tries to actuate its roller blind under these circumstances, the skirt often brakes at the level. It should be noted that these breaks only occur in the event two successive blades are kept substantially edge to edge, in which position they can no longer pivot with respect to each other.
This means that the blades of the skirt length between the rolling-up driving-shaft and the unrolling driving-shaft should be kept steadily apart so that they can at any time pivot with respect to each other, whereby they impede the frost from immobilizing them in an edge-to-edge position.
In addition, since the rolling-up of the skirt is achieved only under the driving in rotation of the rolling-up driving-shaft, the motor must necessarily have a sufficient torque, so as to be able to compensate for the torque produced by total weight of the skirt. Now, this excessive torque is a handicap in the event of clamping of the skirt, e.g., in its upper portion, accommodated in the box. Since it is higher than the mechanical strength of the skirt, it can indeed lead to the breaking of this latter.
Finally, one should note that in order to deliver this high power, the motor should be of an appropriate size. It is therefore also relatively expensive. It is therefore cheaper to adapt the power of the motor to the size of the roller blinds rather than using a standard motor for a series of roller blinds. This does not avoid that this solution, adopted so far, makes stiffer the control of the manufacturer and that of the stocks.